1. Technical Field
The present disclosure relates to a multilayer wiring substrate and a method of manufacturing the same and, more particularly, a coreless multilayer wiring substrate and a method of manufacturing the same.
2. Related Art
The multilayer wiring substrate used to mount the semiconductor element is formed by forming wiring layers in a multi-layered fashion on both surfaces of a core substrate formed of a resin substrate by means of the build-up method, or the like. The core substrate is used as the supporting base of the wiring layers. When the wiring layers are supported by the core substrate, the wiring layers can be formed in a multi-layered fashion through the build-up method, or the like.
Meanwhile, for the purpose of reducing a size of an electronic component such as a semiconductor device, or the like, a reduction in size and thickness is also required of the multilayer wiring substrate. The core substrate occupies about ½ of the multilayer wiring substrate in thickness. Therefore, in reducing a thickness of the multilayer wiring substrate, it is advantageous to form the multilayer wiring substrate only by using the wiring layers without the core substrate. Thus, the multilayer wiring substrate using no core substrate, i.e., the so-called coreless multilayer wiring substrate is being studied.
However, in the coreless multilayer wiring substrate, a shape-retaining property is lowered in contrast to the multilayer wiring substrate having the core substrate. For this reason, a means for retaining a shape of the wiring substrate is needed such that the wiring substrate is not warped. As the method of retaining a shape of the wiring substrate, there are a method of mounting a reinforcing member onto the wiring substrate, a method of preventing a warp by providing a reinforcing layer, a method of using a reinforcing resin material containing a glass cloth as the insulating layer, and others (see e.g., JP-A-2004-186265, JP-A-2007-266136 and JP-A-2001-24338)
From the aspect of a reduction in size and thickness of the multilayer wiring substrate, the method of providing the reinforcing layer or the reinforcing member separately from the wiring layers is not necessarily effective as the method of forming the coreless multilayer wiring substrate. On the contrary, the method of using the resin material containing the glass cloth as the insulating layer can retain the shape-retaining property of the multilayer wiring substrate. Also, there is no need to provide the reinforcing layer as another layer. Therefore, this method can attain a reduction in thickness effectively.
However, according to the resin material containing the glass cloth, in a situation that the wiring patterns should be formed extremely finely, such a problem existed that the glass cloth obstructs a formation of the wiring patterns with high accuracy. Further, when the coreless multilayer wiring substrate is formed using the resin material containing the glass cloth, another structure for achieving a reduction in thickness and preventing a deformation such as a warp is required.